This invention relates to a novel method of manufacturing sulfated cellulose and more particularly to a method of activating cellulose prior to its sulfation.
The U.S. Pat. No. 3,528,963 sets forth the process of causing cellulose prior to its sulfation to imbibe boiling water in order to elevate the sulfation reaction. However, sulfation of cellulose after said imbibition is accompanied with undesirable results such as loss of sulfating agent due to presence of water and hydrolysis of cellulose. The Canadian Pat. No. 921,903 discloses the process of treating cellulose prior to its sulfation with dimethyl formamide (DMF). Further, Japanese Patent Application early desclosed under No. 89786/74 describes the process of treating cellulose prior to its sulfation with lower ketones such as acetone. Another U.S. Pat. No. 3,720,659 adopts the process of dissolving cellulose, before sulfation, in cuprammonium solution, and crystallizing out cellulose in an activated state. The last three prior art methods omit the use of water and indeed eliminate drawbacks resulting from the presence of water in the sulfation reaction system of cellulose, but still are accompanied with the disadvantage that activation of cellulose prior to its sulfation has been experimentally found to be insufficient.
Japanese Patent Application early disclosed under No. 89787/74 provides the process of manufacturing sulfated cellulose which is characterized by introducing hydrochlorides of basic nitrogen compounds into the sulfation reaction system for the smooth progress of cellulose sulfation, thereby providing a clear or hazy aqueous solution containing sulfated cellulose which has a high viscosity and a large degree of substitution (hereinafter abbreviated as DS). DS is measured with respect to the residual radical of glucose and indicated as 3 where substitution is fully carried out. Said disclosed Japanese Patent Application No. 89787/74 indeed has great advantages, but is still accompanied with the drawbacks that amine hydrochlorides are difficult to recover and a large amount of washing solvent has to be used in purifying the reaction product.